House electric



Sept. 30 1924. 1,509,965

A. M. MacFARLAND THERMAL RELAY Filed mz. 17. 1920 Fly 3.

WITNESSES: INVENTOR f/JMWW A//mMmfdr/md l BY W j ATTORNEY Patented Sept. 30, 1924.

UNITED STATES Pe'llszNTOFFICIELA ALLIS M. MACFARLAND, OF PITTSBURGH, PENNSYLVANIA, ASSIGNOR.TO"WIESTING-V HOUSE ELECTRIC & MANUFACTURING COMPANY, A CORPORATION OF PENNSYL- vANrA.

THERMAL RELAY'.

To all whom t may concern.'

Be it known that I, ALLrs M. MACFAP.- LAND, a citizen of the United States, and a residentof Pittsburgh, in the county of Allegheny and State of Pennsylvania, have invented a neiv and useful Improvement in Thermal Relays, of Which the following is g a specification.

My invention relates to thermal relays and particularly to bimetallic thermal relays.

One object of my invention is to provide a relay having a thermaleresponsive device that inherently shall have such heating characteristics as to ensure effective operation, when connected in circuit with a device to be protected, Without the use of auxiliary heating devices..

Another object of my invention is to provide a bimetallic member that inherently shall have high electrical resistance.

Anotherobject of my invention is to provide a relay of the cartridge type that shall have means whereby the thermal elementsI and contact members thereof may be mounted, as a unit, on one ferrule of the cartridge.

l Another object of my invention is to so loop thebimetallic members that a relatively llong member may be disposed Within a short` cartridge.

A further object of my invention is to provide a relay, of the above-indicated character, that shall be simple and inexpensive to construct and effective in its operation.

Heretofore, when thermal relays were used for the protection of electrical apparatus, it was found desirable, especially when the device to be protected consumed a relatively small value of current, to provide a heating element for theV thermal-responsive member. This Was found necessary by reason of the fact that insuliicient heating vvasobtained when the thermal-responsive device was made of such mechanical structure as to ensure effective operation.

In vieiv of the above, I providea bimetallic member of the required mechanical strength to obtain elfective operation and I slit the same alternately lfrom opposite ends thereof to constitute an electrical conductor having relatively high resistance. It will be seen that, With this arrangement, sufficient heat may be generated in a relacured together tivelyl large bimetallic member, by a relamembers, as a' unit, on one ferrule of a device of the cartridge type, inrorder-to ensure, at all times, effective alincment between vthe contact members and consequent accuracy of operation. Looping the bimetallic member permits the disposition of a 'relatively long member Within a relatively short cartridge.

Figure 1 of the accompanying dravvings` is a diagrammatic view of an electric circuitA that includes a thermal relay embodying my invention;

Fig. 2 is a plan view of the bimetallic member shown in the relay in Fig.l 1, and

Fig. 3 is an edge vieiv of the member shown in Fig. 2.

A motor 1, or other electrical translating device to be protected, is provided with current from .a circuit 2 thigoughan interrupter 3. The interrupter 3 is provided with afloiv- 'voltage'holding coil 4 and afspring for actuating'the same when the coil 4 is'de- A energized. The circuit of the coil 4 is con trolled by a thermal relay 6 which isconnected infcircuitV With themotor 1;

The thermal relay 6, as shovvn in Fig. 1', comprises a cylindrical casing 7, tivo end ferrules 8 and 9 and a unitary thermalresponsive device 10. The unitary thermalresponsive device 10 comprises a supporting member 11 to Which is secured al bimctallic 4 member 12 and an insulating block 13 upon Which a contact member 14'is adjustably mounted. A contact member'l is Amounted on the bimetallic member 12 but is insulated therefrom and'is adapted to engage the contact member 14. The supporting member 11 is secured to the ferrule 8 by rivets 16.

The bimetallic member 12 comprises tvvo strips of metal 17 and 18having different temperature coeflicients4 and effectively sein" vface-to-face relation. Slits are cut in the bimetallic member 12 from the respective ends thereof in such manner as to greatlyincrease the resistance to the flow of cu 1rent therethrough. That is, with the bime-tallic member 'slit,""as shownA in Fig. 2, the resistance tothe llovv` of current from the point 19 to -the point 2O is considerably greater than the resistance to the flow of current from one end to the other of the original strip. The point 19 of the member 12 is electrically connected to the supporting member 11, and the point 20 is connected, through a conductor 21, to the ferrule 9 by frictional engagement With a member 22 that is electrically connected to the ferrule 9. The contact member 15 insulated from the bimetallic member l2 and is electrically connected, through a flexible connector 23, to the ferrule 8, through the supporting member 11 topreclude the control current from traversing the strip 12. The ferrules 8 and 9 are adapted to 'be received by ordinary cartridge-fuse clips.

The contact member 14 is connected, through a conductor 24, to a. terminal post 25, which, in turn, is connected, through the coil 4 of the interrupter 3, to a conductor 26 of the circuit 2. It will be understood that the relay 6 is placed in series with the conductor 27 of the circuit 2 in order that the coil 4 may be connected across the circuit.

In order to dispose a long bimetallic member in a short cartridge, the member is so looped, at a point intermediate the ends thereof, that the overall length of the looped member is substantially one-half of the original length.

Since the resistance to the flow of current through the element 12 is relatively high, it ivill readily be seen that the device mav be adjusted to cause disengagement ot the contact members 14 and 15 when a predetermined value of current has traversed the motor 1 for a predetermined interval ot time.

The heating characteristics of thedevice (5V element 12 to cause the same to operate effectively to Cle-energize the coil 4 which permits the spring 5 to open the interrupter and thus disconnect the motor 1 from the circuit. The coil 4, being a low-voltage coil, Will, of course, also permit the interrupter 3 to open When the voltage across the circuit 2 falls below a predetermined value. Since the unit 10, comprising the bimetallic member 12 and the contact members 14 and 15, is mounted on one ferrule of thev device, it will be understood that the necessity for accurate alinement of the ferrules 8 and 9 is obviated, whereby a more accurate device is obtained With less expense.

My invention is not limited to the specific structure illustrated, as it may be modified Without departing from the spirit and scope of the same as set forth in the appended claims.

l claim as my invention:

1. A thermal relay comprising a tubular member of insulating material, ferrules disposed at the respective ends thereof, a supporting member disposed on one ferru'le, a bimetallic member disposed on the supporting member' and looped back to permit a relatively long element to be disposed Within a space of predetermined length, means for connecting one end of the bimetallic member to the opposite ferrule, and a contact member controlled by the bimetallic member.

2. A thermal relay comprising` a cylindrical casing, tivo end ferrules therefor, a slotted bimetallic member supported on one ferrule only and looped to permit a relatively long element to be disposed Within a space of predetermined length, means for connecting` the ends of the bimetallic member to the respective ferrules, and a contact member cont-rolled by the bimetallic member.

A thermal relay comprising a cylindrical casing, Vtwo end ferrules therefor, a slotted bimetallic member supported on one ferrule only and looped to permit a relatively long` element to be disposed Within a space of predetermined length, means electrically connected to one end of the bimetallic member for slidably engaging means electrically connected to one ferrule, and a contact member controlled by the bimetallic member. y

4. A. thermal relay comprising a cylindrical casing, two'end ferrules therefor, a slotted bimetallic member supported on one ferrule only and looped to permit a rela-- tively long element to be disposed Within a space of predetermined length, means electrically connected to one end of the bimetallic member for slidably engaging means electrically connected to one fel-rule, a contact member controlled by the bimetallic member, and an adjustable contact member adapted to be engaged by the former contact member and having means for being connected into an auxiliary circuit.

A thermal relay comprising a cylindrical casing, tivo end ferrules therefor, a bimetallic member of substantially U-shape having the ends thereof connected to the respective ferrules, a contactmember controlled by the bimetallic member, an adjustable Contact member adapted to be engaged by the former contact member until the bimetallic member is heated to a predeteri'nined degree', and means tor connecting the adjustable contact member into an auxiliary circuit.

6. A thermal 'relay comprising tivo end ferrules, a slotted bimetallic .member supported at one end on one ferrule and having the other end thereof so looped as to permit the disposition of a relatively long member in a relatively shortspace, and means for connecting the bimetallic member between both ferrules.

"7. A thermal relay comprising two end ferrules, a looped bimetallic member, a supporting member therefor mounted on one ferrule, aV contact member controlled by the bimetallic member, and an adjustable contact member mounted on the supporting member and adapted to be engaged by the former Contact member, the controlling bimetallic member being so looped as to permit the disposition of a relatively long bimetallic member in a relatively short space and to dispose the co-operating contact members adjacent the supporting member, and means for electrically connecting the bimetallic member between both ferrules.

In testimony whereof, I llave hereunto ALLIs M. MACFARLAND.`

11th day of 

